automotive thermal paste????

[C0RR0SIVE]

Nah, don't work at the dealer, just have a GMC Sonoma, and a Haynes manual, along with a few other books that also cover your Jimmy, as well as 10+ years working on several dozen different cars for family and friends. Almost have my own little garage here with cars in and out daily now.

If you could get me a good picture of the engine bay from an overhead position, I would know for sure what kind of ignition system you have, pretty sure it's EDI from your description.

Aside from ignition related components, we could have an issue with proper fuel delivery, but I would prefer all electrical components on the spark side are operational before we poke at possible fuel delivery issues.

BTW, while most hate Haynes booklets, I find they are rather great to have handy because they DO list the original factory specs for everything - which can also be a big drawback as over time the factory changes specs. But usually when buying parts, if a spec has changed, they include papers with the parts that list what models those specs had changed on. Might want to think about picking one up some day, they aren't that cheap, but they are a very valuable resource to have if you plan on keeping a vehicle for more than a year or two.


As for your wifes car, if it has ultra high compression, or a really fancy ignition system, it could very well take into account fractions of a degree for fuel temp to measure out very precise amounts of fuel, or even adjust the voltage for firing the plus, or if it has VVT of some form, adjust that for a slightly different burn. Manufactures are having to measure every potential variable these days because of increases in required fuel economy from the government. So IF you have a fuel temperature probe that's not measuring right, consider replacing it at some point in the near future, heck, even an air intake temp sensor can allow a car to run, but throw fuel mileage off. Our 97 towncar (it's in rough shape now though) had a fault air intake temp sensor, couldn't get above 18mpg, and wasn't triggering the CEL. Replaced that, now it gets upwards of 24mpg, and that's on an old big v8 engine. Wouldn't think it matters much since it has a MAF, but it really does.


ANYWAYS, let me know what you DO find, and depending on whats found, I will post up how to check the "timing" for the ignition. Rather stupid they used that method to time the spark, but I guess it's an old tested method that just works if you have ever messed with such things.

 

[XWrench3]

well,i checked the wires one at a time, so as not to take any chance of re-installing them in the wrong order. all of them were under 5k ohms, except one, which made it all the way up to 6.25 (approximate) (analog meter) k ohms. so those seem fine. the plugs looked fine as well, the crisp edge on the electrodes has rounded a bit, but that i feel is normal after 35,000 - 40,000 miles or so. the ignition coil measured fine, with the exception of the primary side. which measured just short of 1 ohm instead of the .2-.5 ohms you listed. so that looks suspect to me at this point. now for the (not so) funny part. after doing all of this, i took it for a drive to help a friend work on his motorcycle. its only about 25 miles to his home from my place, but it is straight down the highway from our home. the truck never missed a beat all the way there and back. so i am not sure if it was remounting the ICM with new grease, or if maybe i had a bad connection someplace. or if it is just a fluke, and the next time i drive it it will start acting up again. i hate intermittent problems, other than leaving you stranded, just dieing outright is a lot easier to fix. i saw online that i can buy both the ignition coil and ICM as a unit. so if this starts acting up again, i think that is the place i will start replacing things. i can kill 2 birds with one stone so to speak. and the price was way lower than buying each one separately.
you mentioned a way to set the timing. which intrigues me. i didn't think you could adjust the timing on a crank triggered ignition system. at least w/o a laptop and the correct "tuning" software.
as far as my wifes car goes, i have no idea what the fuel mileage is. she can not manage to write down the miles on the odometer when she fuels up, or even remember to push the reset button n the trip meter. i am sure if i didn't keep track of the mileage of the car, it MIGHT get an oil change once a year. but ONLY IF the engine ran out of oil! her best friend did that exact thing, 3 times in a row! how that engine even runs is beyond me.

 

[C0RR0SIVE]

Heh, the females in my family are the same way.

You can't exactly adjust the timing, but that rotor, it's apparently semi adjustable, as in, it can be set wrong very easily during an install, it is worth checking it's time. Let me know if you want what my book says and I will type it out and post it up.

Honestly, if it's just shy of 1Ohm on the primary side, your ICM is having to work FAR FAR harder to pump the required low voltage and amperage through it to get the needed spark. Lets say it pumps out 12v at 10A, that's 120W, and it has to step that up to several thousand volts for the proper spark. Well, the primary side has doubled it's resistance in essence and now the ICM is having to pump 12v @ 15+ amps. This can quickly damage the ICM, as well as cause a strange intermittent random misfire. If you are able to get quality AC Delco parts (sorry, I trust only AC Delco coils and control modules), I would go ahead and replace just the coil, as the ICM seems OK at this point in time since it's still firing. Also, temperature can have a major impact on a coils performance if the coil is on its way out. That fine copper wire inside it probably has a few broken spots, and temperature will cause that copper to expand/contract in such a way that some days it might work fine, and one day it may miss, then the next it could probably die for good.

But yeah, I highly suggest replacing the coil, and before putting the new coil on, test the new coil primary and secondary sides.

 

[XWrench3]

its funny how things have changed over the years. i remember buying an Accel Super Coil to get more voltage for my hot rod. the coils on this Jimmy is 1/3 the size, and probably delivers double the voltage of that old Super Coil. and at 1/6 the size.
it almost sounds like the ICM is a step up coil for the ignition coil. but that does not make a lot of sense. although it would spread the heat out over two components. but it sounds like a lot of expense just to do that.
if i am going to replace the coil, i think it would be best to replace the ICM as well at the same time. if it is working extra hard to make up for shortcomings in the ignition coil, AND it had a compromised cooling path, it seems very likely to me it has been compromised as well. and i HATE being stranded, especially in c-c-cold weather. this truck is beginning to act like a Ford (fix or repair daily) car. this will be the 5th pay check in a row with money going into the truck. and i know i have at least 2 more issues with it. if i could afford it, i would just trade it in on a new Toyota. but i would need to win the lottery to do that.

 

[C0RR0SIVE]

Strangely, I don't know why that thing even has an ICM to be honest, as those are usually seen when you have multiple coils on an engine, guess it has to do with a rather rapid on/off cycle that it has to endure since one coil and one switch is what's firing your 6 cylinders instead 3+ switches. Guess a typical relay just wouldn't cut it.

Typically the ICM gets fed data from the ECM and is nothing more than a large switched relay, usually you have 12V+ going to it from the battery, signal wires for each coil from the ECM, and a ground. It then acts like a normal high current relay that directs power to each coil as it's told by the engine computer, and then the coil is what does the step up. It's simpler to have a single relay unit instead of building a relay into each coil. It really cuts down on the amount of wiring, as well as production cost overall.

But hey, if it's cheap, replace it if you want, I still think you should try just a coil first. The ICM on my car is about $250, then again, it's also running 6 separate coils, at the tune of $75 per coil.

 

[XWrench3]

in my chosen industry (motorcycles) we do not see many failed ignition coils, even firing double spark plugs @ 14,000 rpm. even on air cooled 14.000 rpm engines. i can not ever recall an ICM on a bike. just the cdi box, and a coil or a pair of coils. and the coils are normally mounted directly over the cylinder head. talk about heat soaked! but, they seldom run gaps of more than .040" also, which i am certain helps. i can not say what has happened in the last 8 or 9 years though, as i have not kept up with it. i was forced into early retirement (disability) due to an injury.
i did find extremely low priced coil/icm combos on ebay as low as $40.00. and just an AC Delco ignition coil as low as $25.00 (buy it now) so they are not terrible expensive. but an AC Delco ICM is $125.00! aftermarket ICM's start as low as $10.00! but you will not find one of those on my vehicles unless i get stranded, and that is all that is available to get me home. a good (BWD) aftermarket ICM is about $60.00, which i can live with, and feel comfortable that i will not be left stranded. so that is the way i will go.